Edge position measurement is an important requirement in continuous web manufacture processes. There have been a number of edge measuring systems disclosed in the prior art and in the trade literature. The vast majority of these systems operate by optically, pneumatically or physically sensing the edge of a continuous web, and providing a signal to correct the position of the web feeding apparatus with respect to the edge of the web.
Optically based edge measurement systems are expensive and complicated. Prior art dielectric edge sensor technologies have also had a number of technical limitations. One of the main problems associated with conventional edge sensor technologies which depend upon the dielectric response of the base material of the moving web, is that imperfections or anomalies in the web material may vary over the surface area of the web. These imperfections and anomalies, which may exist at various portions of the web, prevent a proper reading and may yield an incorrect measurement. Accordingly, when conventional edge sensors err, they cause an improper shift in the web position or devices which track edge position.
A number of prior art patents have been directed to the problem of properly placing the edge of the uptake roll of a continuous web and in adjusting the position of the web. U.S. Pat. No. 4,381,586 discloses a control system for maintaining a constant predetermined transference with a continuous elastic or extensible web while the web travels longitudinally, and while simultaneously transversely aligning the longitudinally moving web and register with a transversely extending work station which extends across the web at a preset location. The system disclosed in this patent relies upon the use of an optical counter which adjusts the position of a work table in response to lateral movements of the web. This control system is most clearly shown in FIG. 3 and described at column 4, lines 25-70 and utilizes pneumatic pressure sensors, identified by reference numerals 35 and 36.
U.S. Pat. No. 4,888,717 discloses a method and apparatus for controlling the lateral position of a moving web of material having a central longitudinally web access extending generally parallel to the direction of movement of the web so as to maintain the central longitudinally extending access of the web at a substantial constant lateral position. This position is fixed longitudinally and is associated with a fixed web alignment station. As most clearly shown in FIG. 19 and at column 20, this invention utilizes an optical eye in conjunction with an encoder to adjust lateral position of the web in order to make lateral adjustments.
U.S. Pat. No. 4, 956,964 is directed to an adjustable pouch form, fill seal machine. The web is folded upon itself and transversely sealed. The invention incorporates lateral adjustment mechanism which uses an optical counter. Finally, U.S. Pat. No. 5,345,863 is directed to continuous web printing apparatus which includes a mechanical lateral shift device.
None of the prior art discloses or suggests an edge position sensor in combination with a gauge which measures a web property such as thickness, density, composition, moisture or temperature. It would be desirable to provide an edge sensor mechanism which includes a gauge. Such a device would enable the rapid and accurate placement of a web on an uptake roll and would compensate for anomalies in the material, caused by changes in web property. Such a device would compensate for the inherent problems associated with prior art web sensing technologies and would be an improvement over optical, mechanical and pneumatic devices which are often expensive and inaccurate.